This invention relates generally to dual valve members, and more particularly to controlling fluid flow in a fuel injector using a dual valve member.
Hydraulically actuated fuel injectors having a single control valve that controls fluid flow to both a spool valve and a direct control needle valve included in the injector body are known in the art. One example of such a fuel injector is disclosed in U.S. Pat. No. 5,738,075 issued to Chen et al. on Apr. 14, 1998. While fuel injectors such as those disclosed in Chen et al. have performed adequately, there remains room for improvement. For instance, because control of fluid pressure to the spool valve control surface is coupled to fluid pressure to the needle valve control surface, undesirable interactions can occur. In addition, the seated pin included in the control valve must have a sufficient size and travel distance to allow the fuel injector to perform as desired when operating under cold start conditions. However, the size and travel distance of the seated pin are limited by the force available from the actuator to overcome the flow and/or viscosity forces present and, in addition, by the required response time. Finally, a substantial amount of fluid must be displaced past the seated pin whenever the spool moves, which runs counter to the desire for short travel distances and times.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a fuel injector includes an injector body that defines a first passage, a second passage, a variable pressure passage, a pressure communication passage and a nozzle outlet. The variable pressure passage is fluidly isolated from the pressure communication passage. A needle valve member is movably positioned in the injector body and has a closing hydraulic surface exposed to fluid pressure in the pressure communication passage. A dual valve member is positioned in the injector body and has a first valve member and a second valve member. An electrical actuator is operably coupled to the dual valve member. The dual valve member is movable between a first, second and third position.
In another aspect of the present invention, a fuel injection system includes a high pressure source, a low pressure reservoir and a source of fuel. At least one fuel injector is provided that has an injector body that defines a fuel inlet fluidly connected to the source of fuel, a high pressure passage fluidly connected to the high pressure source and a low pressure passage fluidly connected to the low pressure reservoir. The injector body also defines a variable pressure passage, a pressure communication passage and a nozzle outlet. The variable pressure passage is fluidly isolated from the pressure communication passage. A needle valve member is movably positioned in the injector body and has a closing hydraulic surface that is exposed to fluid pressure in the pressure communication passage. A dual valve member is positioned in the injector body and has a first valve member and a second valve member. An electrical actuator is operably coupled to the dual valve member. The dual valve member is movable between a first, second and third position.
In yet another aspect of the present invention, a method of injecting fuel includes a step of providing a fuel injector that has an injector body that defines a high pressure passage, a low pressure passage, a variable pressure passage, a pressure communication passage and a nozzle outlet. The injector includes a dual valve member and a needle valve member. The variable pressure passage is fluidly isolated from the pressure communication passage. A closing hydraulic surface of the needle valve member is exposed to fluid pressure in the pressure communication passage. The dual valve member is biased to a first position in which the variable pressure passage is open to one of the high pressure passage and the low pressure passage, and the pressure communication passage is open to the high pressure passage. The variable pressure passage is then opened to an other of the high pressure passage and the low pressure passage. The nozzle outlet is then opened, at least in part by moving the dual valve member to a third position opening the pressure communication passage to the low pressure passage. Next the nozzle outlet is closed, at least in part by opening the pressure communication passage to the low pressure passage. The variable pressure passage is then opened to the one of the high pressure passage and the low pressure passage.